Re: block 8080, but redirect from 80 to 8080

[Pascal Hambourg <pascal.mail@plouf.fr.eu.org>]

Hello,

Dean Hiller a écrit :
> I would like block all traffic to port 8080 except that which was 
> redirected in the nat table from port 80 to 8080.
> I have a default policy of DROP on incoming.  The following is what my 
> iptables file currently has and this works, EXCEPT that 8080 is left 
> open to anyone....
> 
> *nat table.....
> -A PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8080
> 
> *filter table.....
> -A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j 
> ACCEPT

This rule seems useless : port 80 has been redirected to port 8080 in 
the PREROUTING chain, so no valid packet will ever enter the INPUT chain 
with destination port 80.

> -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 8080 
> -j ACCEPT
> 
> but anyone can go to http://<machine>:8080 which I want to disallow.  
> How can I fix that?

Quick and dirty :
Drop the undesired packets in the PREROUTING chain of the 'mangle' 
table, before REDIRECT occurs.

iptables -t mangle -A PREROUTING -p tcp --dport 8080 -j DROP (or REJECT)

Better :
Mark the desired packets in the PREROUTING chain of the 'mangle' table 
before REDIRECT occurs and accept only the marked packets in the INPUT 
chain of the 'filter' table.

iptables -t mangle -A PREROUTING -p tcp --dport 80 -j MARK --set-mark 1
iptables -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp \
   --dport 8080 -m mark --mark 1 -j ACCEPT